1. Field
This relates generally to semiconductor processing and, more specifically, to methods for multi-energy ion implantation.
2. Related Art
Ion implantation is an important process in the production of integrated semiconductor devices where dopant ions such as boron, phosphorus, arsenic or the like are implanted into a semiconductor substrate to modify the conductivity of the substrate. Certain applications, such as the doping of semiconductor fin structures in the fabrication of FinFET devices, may require a multi-energy ion implantation process to achieve desirable uniformity and thus desirable device performance. In a multi-energy ion implantation process, an ion implanting system performs a set of implants on a target (e.g., a semiconductor wafer having a semiconductor device formed thereon) where each implant is performed at a different energy.
Conventionally, the implant energy for a multi-energy ion implantation process is controlled by adjusting the ion source and the extraction assembly conditions. For example, the implant energy may be increased by increasing the extraction voltage while increasing the distance between the ion source and the extraction electrode. Additionally, the dopant gas flow rate and the source magnetic field may be adjusted to achieve the desired ion beam current. Adjusting the ion source and extraction assembly conditions optimizes the ion beam current for each implant, thereby extending the life of the ion source. However, changing the ion source and extraction assembly conditions also destabilizes the ion beam where the ion beam requires up to several minutes to re-tune and re-stabilize before it can be used to implant ions into a target. In order to reduce the frequency at which the ion source and extraction assembly conditions are changed, conventional multi-energy ion implantation processes may, for example, implant every target in a production lot at a first energy prior to changing the ion beam to a second energy. Each target in the same production lot may then be implanted at the second energy. However, target handling times are increased because each target is transferred into and out of the ion implanting system for each implant energy. Thus, conventional multi-energy ion implantation suffers from low throughputs and may not be a manufacturable solution for semiconductor device production.